Apparatus for electrically filtering paraffins



\ Nov. 11, 1952 K, 5 2,617,763

APPARATUS FOR ELECTRICAL-LY FILTERING PARAFFINS Filed April 8, 1949 JffOAA Ey Patented Nov. 11, 1952 APPARATUS FOR ELECTRICALLY FILTERING PARAFFINS Karl A. Fischer,Washington, D. 0. Application April 8, 1949, Serial No. 86,373

3 Claims. (01. 204--299) (Granted under the act of March 3, 1883, as

The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to an improved electrostatic filter and, more particularly, to improved electrostatic filters and their application to the separation of solids dispersed in liquids as, for example, paraifinic crystals in the dewaxing of oils or the like.

The filtration of solids from liquids in the presence of a filter medium assisted by an electrical field is known as such. However, the known processes operate efi'iciently in dewaxing oils or the like, only under high voltage well above a few thousand volts. A direct current is generally used to efiect orientation of the particles and eventually conglomeration and neutralization of oppositely charged suspended particles to provide a cake upon the filter medium. Further, it has been generally presumed that heavy and dense filter media gave better results, relative to filtrate pour points. These dense filter mediums are detrimental to filtration velocity and, therefore, reduce plant capacity.

To overcome the use of dense filter media, filtration apparatus has been designed as illustrated in my copending application Serial No. 26,913, filed May 13, 1948, to operate as electric condensers in which the filter medium is a dielectric between or surrounded by oppositely charged conductors.

It has been discovered that contrary to the application of controlling porosity of the filter or of using specially designed dielectric filters of the condenser type, separation of solids from liquid dispersions can be effected with great ease byan electrostatic field generated by oppositely charged conductors acting as the filter medium.

It is,accordingly, an'object of this invention to provide improved electrostatic filters amended April 30, 1928; 370 0. G. 757) It is another object of this invention to pronating current produced at low. voltages on the order of 1000 and considerably less.

Other objects and advantages of this invention will be apparent fromthe following description when taken in conjunction with the accompanying drawings wherein,

Fig. l is an illustrated top plan view of a filter embodied in this invention;

Fig. 2 is an enlarged cross-sectional, partial end view of Fig. 1; and

Fig. 3 is an enlarged partial top plan view of my Fig. 1.

Fig. 4 is a filter pan and modified filter.

One form of the present invention, as illustrated herein, comprises filter media I0 formed of a pair of electrical conductors interwoven to produce a weave consisting of warp I I and filling or shute I2. The warp II, for example, is an electrical conductor I3, covered by an insulating body I4. The insulation I4 is a coating of an oil and solvent insoluble material in the nature of vinyl polymers, nylon, or the like. The filling I2, for example, is an electrical conductor I5,

covered with electrical insulating material I6, of

oil and solvent insoluble material as vinyl polymers, nylon, or the like.

As illustrated in Figures 1 and 3, the conductors I3 of the warp II are attached to a common electrical conductor I! covered by insulation II' illustratively charged by a direct current source, through a conventional voltage regulator (not shown), from the positive lead l8, and the conductor wires I5 of filling I2, are attached to the like common electrical conductor (not shown) covered by insulation I9 and adapted to be grounded or attached to the negative pole of a charging system throughlead 2D. The insulation I1 and I9 may be similar to the heretofore described insulation I4 and I6.

The above-described filter media may be installed in apparatus of the characterillustrated in my copending application within conventional filters such as rotary or stationary pan, leaf or drum filters, to provide a smooth surfaced filter medium wherein strong electrical fields induced by low charges of only a few hundred volts or less are created at the point of filtration. With the warp and the filling weave as above indicated, in the form of a plain twill, Dutch or braid weave of a highly porous character, the relative porous area between the threads may be of comparatively greater size than the wax crystalline material or the like, which is to be separated. Ordinarily as may be expected when no charge is placed on the filter, incomplete and not fully satisfactory separation of solids and liquid takes place. However, when a charge of from volts ,ter units utilizing the field effectof oppositely Further, n1

charged conductors may be formed with conductors of the character herein indicated, insulated from each other and irregularly arranged as by intertwining, twisting or meshing to form a plurality of irregularly arranged interstices. In this arrangement, an electrical field of greater depth is obtained, although laminated layers of woven conductors will produce a like efiect.

It is the usual practice in the oil dewaxing and. wax producing plants to install a plurality of filters of the pan, leaf or drum type, in series or in parallel, according to the desired. plant arrangement and capacity. As may be expected from the standpoint of efliciency, the operation of a wax filter plant is concerned with temperature, dilution, character of solvent, and rate of filtration. To produce wax cakes or oils having specific pour point characteristics,- the first three factors can be determined and controlled with certainty. whereas the filtration rate, while a predominant factor in, determining plant throughput and specific pour point values, is frequently variable and inaccurate. With the filter structure as herein provided, a-control of current by maintenance of a predetermined voltage with a suitable voltage regulator provides means for influencing the percentage of wax separation which, in turn, automatically affects control of pour point values.

For example, Wax crystals in propane-deas phaltized residual oilsin a non-conductive dichlorethane solvent, chilled to 25 C. by a conventional method, are smaller in average size than the diameter of the openings in the weave formed by the electrical conductors l3 and 95. Obviously, the filter structure without an electrical charge will al-lowpart oi the crystals to pass through the filter. However, by placing a charge of only a dozen to a=few hundred volts, the crystals are retained by the filter-and the filtrate pour point is improved by 4 F. to F. with the application of from approximately 50 to 500 volts. In some instances, only a few hundred volts and. appreciably less than a thousand will produce an improved filtrate of better pour point value than standard filtration methods. Further, for some filtering operations the rate of filtration is increased by 10 percent to substantially more, due to the fact that wider mesh filter cloths can be taken.

While I have heretofore described in-detail a specific construction, it is likewise possible, as diagrammatically illustrated in Fig. 4, to provide a filter structurewhich separates in a similar manner by utilizing in the, weave a Warp 2! consisting of an exposed metal surface which may be, for example, electrically conductivetextile fibres or flexible metalstrands and the like, with ashute or filling-22 consisting of a conductor core, of the character above described or covered by conventional insulating fibres. insulating plastic. or enamels. For utilization of such filter media in the separation of parafiinic crystals or like solids, the conductor surface supporting medium of warp 2i and insulation coatings for fill.

ing 22 are of material insoluble in the filter stock.

Figure 4 also illustratesa filter structurefor separating wax from oils and consisting of vertical shell 23' closed at itslower end by filter pad 2 constructed as indicated above or formed in any manner as herein described. This filterpad 24, being formed of conductorspis self-supporting when mounted by holding ring 25 on flangedportion 25' Thelead I8 feeds the insulated-conductors 22 through a voltage regulator 26 and a common or unitary electrical connection of the character described with respect to Fig. 1. The ground 20 is likewise connected to the conductors 2|. When a field in the fi ter pad 24 is energized by low voltages, the filter pan is ready to operate in a conventional manner or in a manner as described in the above-mentioned application. For example, a chilled solution is passed into the shell 23 from feed pipe 21 through control valve 28, crystalline and solid materials are deposited on filter pad 24 as the filtrate flows into receiving receptacle 29 from where it is discharged through outlet passageway 30 by control valve 3|, as in conventional processes. The receptacle 29 may be integral with the holding ring 25 which is illustratively mounted by screw threads 32 or otherwise supported in the conventional manner for such filter units.

Likewise, while the filter media herein described have been illustrated for use'with separation of parafiinic crystals, they are also applicable for use in theseparation of aqueous suspensions or conductorliquidbodi-es when at least either the warp or filling has been insulated by a suitable insoluble insulator coating. Preferably in any direct current installation, it will be desirable to provide the positively charged conductor with insulation, inasmuch as the negative conductor may be grounded to the body of the container. Similarly, it is preferable, when alternating current is to be utilized with the filter media in the presence ofaqueous' or conductor liquids. to insulate both the warp and the filling in the manner as herein described.

With the above-described apparatus, it has been discovered that a control of pour point values can be made by control of applied voltages. Further, with the coatings provided either in the nature of a metallic or resinous material, a smooth contacting surface for the Waxed cake is provided to afiord complete separation of the filter cakes. In addition, it has been discovered that frequently, colloidal suspensions can be broken down under the condition of either A. C. or D. C. currents at low voltages on the order of from only a dozen or even less to a few hundred volts.

With the method and apparatus as herein disclosed, it will be'obvious that an improved electrostatic filter utilizing properly insulated conductors as'a filter medium may be used to produce an electrostatic field toadvantage for the separation of solid materialfrom liquids and that structural modifications may be made wherein oppositely charged conductors produce a filter medium which falls within the scope of the appended claims.

I claim:

l. An electrostaticfilter comprising a woven fabric-like sheet material of insulated, conductor warp threads and non-insulated-ccnductor filling ductors positively, and electrical attachment REFERENCES CITED means chargmg 594d sgcond Set of conduc' The following references are of record in the torsnegatlvelyfile of this patent:

3. An electrostatic filter cloth comprising an electrically conductive set of warp threads, an 5 UNITED ATES PATENTS electrically conductive set of filler threads inter- Number Name Date woven with said warp threads, at leas 0116 Set Of 1,333,838 Csanyi Mar. 16 1920 threads being insulated, electrical attac m 2,031,214 Fisher Feb,18 1936 means for charging one of said sets of threads 2,107,770 Wade Feb. 8 1938 positively, and electrical attachment means for 10 2,292, 0 Buckman t 1 Aug 94 Y charging the other of said Sets Of threads 2,450,016 Pinkel Sept. 28 1948 atlvely. 2,478,934 Morse Aug. 161 1949 KARL A. FISCHER. 

1. AN ELECTROSTATIC FILTER COMPRISING A WOVEN FABRIC-LIKE SHEET MATERIAL OF INSULATED CONDUCTOR WARP THREADS AND NON-INSULATED CONDUCTOR FILLING THREADS, SAID WARP THREADS BEING ATTACHED TO A COMMON ELECTRICAL POLE AND SAID FILLING THREADS BEING ATTACHED TO A COMMON ELECTRICAL POLE OPPOSITE POLARITY, WHEREBY THE WARP THREADS MAY BE POSITIVELY CHARGED AND THE FILLING THREADS NEGATIVELY CHARGED. 